1. Field
Example embodiments generally relate to systems and methods for disposing of one or more radioactive components from nuclear reactors of nuclear plants. Example embodiments also relate to systems and methods for disposing of one or more radioactive components from Boiling Water Reactor (“BWR”) nuclear plants. The systems and methods may be particularly beneficial in reducing critical path time during a plant outage (e.g., refueling outage), reducing or eliminating the need for substantially horizontal transfer of the one or more radioactive components, and/or reducing radiation exposure to personnel related to the systems and methods for disposing of one or more radioactive components. The systems and methods also may be used in other types of nuclear plants whose nomenclatures and precise functions may depend on the specific type(s) and/or manufacture(s) of the nuclear plants.
2. Description of Related Art
FIG. 1 is a sectional view, with parts cut away, of reactor pressure vessel (“RPV”) 100 in a related art BWR. During operation of the BWR, coolant water circulating inside RPV 100 may be heated by nuclear fission produced in core 102. Feedwater may be admitted into RPV 100 via feedwater inlet 104 and feedwater sparger 106 (a ring-shaped pipe that includes apertures for circumferentially distributing the feedwater inside RPV 100). The feedwater from feedwater sparger 106 may flow down through downcomer annulus 108 (an annular region between RPV 100 and core shroud 110).
Core shroud 110 may be a stainless steel cylinder that surrounds core 102. Core 102 may include a multiplicity of fuel bundle assemblies 112 (two 2×2 arrays, for example, are shown in FIG. 1). Each array of fuel bundle assemblies 112 may be supported at or near its top by top guide 114 and/or at or near its bottom by core plate 116. Top guide 114 may provide lateral support for the top of fuel bundle assemblies 112 and/or may maintain correct fuel-channel spacing to permit control rod insertion.
The coolant water may flow downward through downcomer annulus 108 and/or into core lower plenum 118. The coolant water in core lower plenum 118 may in turn flow up through core 102. The coolant water may enter fuel assemblies 112, wherein a boiling boundary layer may be established. A mixture of water and steam may exit core 102 and/or may enter core upper plenum 120 under shroud head 122. Core upper plenum 120 may provide standoff between the steam-water mixture exiting core 102 and entering standpipes 124. Standpipes 124 may be disposed atop shroud head 122 and in fluid communication with core upper plenum 120.
The steam-water mixture may flow through standpipes 124 and/or may enter steam separators 126 (which may be, for example, of the axial-flow, centrifugal type). Steam separators 126 may substantially separate the steam-water mixture into liquid water and steam. The separated liquid water may mix with feedwater in mixing plenum 128. This mixture then may return to core 102 via downcomer annulus 108. The separated steam may pass through steam dryers 130 and/or may enter steam dome 132. The dried steam may be withdrawn from RPV 100 via steam outlet 134 for use in turbines and other equipment (not shown).
The BWR also may include a coolant recirculation system that provides the forced convection flow through core 102 necessary to attain the required power density. A portion of the water may be sucked from the lower end of downcomer annulus 108 via recirculation water outlet 136 and/or may be forced by a centrifugal recirculation pump (not shown) into a plurality of jet pump assemblies 138 (only one of which is shown) via recirculation water inlets 140. Jet pump assemblies 138 may be circumferentially distributed around core shroud 110 and/or may provide the required reactor core flow.
As shown in FIG. 1, a related art jet pump assembly 138 may include a pair of inlet mixers 142. A related art BWR may include 16 to 24 inlet mixers 142. Each inlet mixer 142 may have an elbow 144 welded to it that receives water from a recirculation pump (not shown) via inlet riser 146. An example inlet mixer 142 may include a set of five nozzles circumferentially distributed at equal angles about the axis of inlet mixer 142. Each nozzle may be tapered radially inwardly at its outlet. Jet pump assembly 138 may be energized by these convergent nozzles. Five secondary inlet openings may be radially outside of the nozzle exits. Therefore, as jets of water exit the nozzles, water from downcomer annulus 108 may be drawn into inlet mixer 142 via the secondary inlet openings, where it may be mixed with coolant water from the recirculation pump. The coolant water then may flow into diffuser 148.
FIG. 2 is a top plan view of a core 200 in a related art BWR. Core 200 may include fuel bundles 202, peripheral fuel bundles 204, and/or control rods 206. Two or more of fuel bundles 202 may be included in fuel bundle assemblies 208. Core 200 may include, for example, hundreds or thousands of fuel bundles 202 and/or tens or hundreds of peripheral fuel bundles 204. As shown in FIG. 2, for example, core 200 may include approximately one thousand and twenty-eight (1,028) fuel bundles 202, approximately one hundred and four (104) peripheral fuel bundles 204, and/or approximately two hundred and sixty-nine (269) control rods 206.
The distribution of fuel bundles 202, peripheral fuel bundles 204, and/or control rods 206 in core 200 may or may not be symmetric. Additionally, if symmetry exists, it may include one or more of mirror-image symmetry, diagonal symmetry, rotational symmetry, translational symmetry, quadrant symmetry, and octant symmetry. As shown in FIG. 2, for example, one or more control rods 206 may be disposed in or near a geometric center of core 200.
Core 200 also may include one or more types of neutron monitors. These monitors may include, for example, one or more source range monitors, one or more intermediate range monitors, and/or one or more power range monitors. In a related art BWR, the one or more source range monitors may be fixed or movable. Similarly, in a related art BWR, the one or more intermediate range monitors may be fixed or movable.
At least some of the overall range of a related art source range monitor (“SRM”) and/or a related art intermediate range monitor (“IRM”) may be covered by a startup range neutron monitor (“SRNM”) or wide range neutron monitor (“WRNM”). Similarly, at least some of the overall range of a related art intermediate range monitor and/or a related art power range monitor (“PRM”) may be covered by a local power range monitor (“LPRM”). In a related art BWR, the SRNMs and/or the LPRMs may be fixed.
Core 200 may include, for example, tens of SRNM detectors and/or tens or hundreds of LPRM detectors. Although not shown in FIG. 2, core 200 may include, for example, approximately twelve (12) SRNM detectors. As shown in FIG. 2, for example, core 200 may include approximately two hundred and fifty-six (256) LPRM detectors in approximately sixty-four (64) LPRM assemblies 210. For example, one or more LPRM assemblies 210 may include four LPRM detectors (i.e., each LPRM assembly 210 may include four LPRM detectors).
FIG. 3 is a simplified schematic cross-sectional view of a reactor cavity of a related art BWR, while FIG. 4 is a schematic top plan view of a section of a reactor core in a related art BWR. As shown in FIG. 3, in-core instrument 300 may include an in-core part 302, approximately 15 feet in length (about 4.5 meters), of relatively higher radioactivity, and/or an out-of-core part 304, approximately 27 feet in length (about 8 meters), of relatively lower radioactivity. In-core instrument 300 may be withdrawn from an operative position in reactor core 306 by conventional means and/or may be suspended, by an end, from a conventional equipment-handling crane (not shown), with in-core part 302 uppermost.
First temporary storage container 308 and/or second temporary storage container 310 may be provided in reactor core 306. First temporary storage container 308 and/or second temporary storage container 310 may have outer dimensions substantially identical to either a control rod guide blade 400 (FIG. 4) or a core grid cell 402 (FIG. 4) of one control rod 404 and four fuel assembles 406 (FIG. 4). First temporary storage container 308 and second temporary storage container 310 may extend between and may be temporarily supported by top guide 312 and fuel support plate 314. A remotely operated cutting device 316 may be superposed on first temporary storage container 308.
In-core instrument 300, which may be vertically aligned with first temporary storage container 308, may be lowered until a portion 408 of out-of-core part 304 is within first temporary storage container 308. Cutting device 316 may then be operated to sever the portion of in-core instrument 300 within first temporary storage container 308. In-core instrument 300 may then be lowered further, until another portion 408 of out-of-core part 304 is within first temporary storage container 308, and cutting device 316 may again be operated to sever the portion 408 of in-core instrument 300 within first temporary storage container 308. This proceeding may be repeated until all of out-of-core part 304 of in-core instrument 300 is within first temporary storage container 308. Preferably, out-of-core part 304 may be cut into three portions 408.
With out-of-core part 304 thus removed, the remainder 410 of in-core instrument 300, i.e., in-core part 302, may be lowered into second temporary storage container 310.
Now temporary storage container 308 and second temporary storage container 310 may be removed from reactor core 306 by the equipment-handling crane.
It is to be noted that the entire removal procedure for in-core instrument 300 may be performed beneath a protective water shield (e.g., beneath a minimum 5-foot depth (about 1.5 meters)).
A second cutting device (not shown) may be disposed on second temporary storage container 310 so as to permit cutting in-core part 302 of in-core instrument 300 into sections, in the manner of out-of-core part 304. Alternatively, after severance of out-of-core part 304 from in-core instrument 300, in-core part 302 may be removed from the reactor cavity directly, without use of a temporary storage container.